Method for porcelain enameling mufflers and the like



W. E. PIERCE April 7, 1964 METHOD FOR PORCELAIN ENAMELING MUFFLERS AND THE LIKE 2 Sheets-Sheet 1 Filed June 20, 1961 34, I I 22 M2 11.22

INVENTOR 1444 .a MM ZP/E/PC 5 ooaoaOO ATTORNEYS April 7, 1964 w. E. PIERCE 3,127,951

METHOD FOR PORCELAIN ENAMELING MUFFLERS AND THE LIKE Filed June 20, 1961 2 Sheets-Sheet 2 INVENTOR 1 A2 6 M4 4 09M EHE'RCE W WM United States Patent 3,127,951 METHOD FOR PORCELAIN ENAMELING MUFFLERS AND THE LIKE William E. Pierce, Railnor, Pa., assignor to Porcelain Enamel Institute, Inc., Washington, D.C., a c'orporation of Illinois Filed June 20, 1961, Ser. No. 118,294 12 Claims. (Cl. 181-61) This invention relates to mufilers for internal combustion engines and more in particular to improvements in the coating of mutilers interiorly with porcelain enamel.

The destruction of mufilers for internal combustion engines by exposure to exhaust fumes and high temperatures is a well-recognized problem. Further, the corrosive effects of water and other combustion products, such as lead bromide from leaded gasoline, on the metal pipes, baffles, and other interior parts of a muffler will, in time, destroy these parts so that the muffier becomes useless. In order to overcome this problem, the coating of mufilers interiorly with porcelain enamel has been suggested and carried out with varying degrees of success. I These coatings are made from conventional frits and when properly bonded to the metal surfaces they form a very effective continuous corrosion-resistant layer. I

The usual method of applying these porcelain enamel coatings to any metal surface includes the steps of dipping the object to be coated in a conventional slip of the frit material, removing the object from the slip, drying, and then firing at high temperatures to fuse the coating into a smooth continuous porcelain enamel.

In applying this conventional coating method to a muliler, a completely assembled mufiler is dipped into a bath of the slip, the latter entering the inlet and outlet exhaust openings and flowing along the interior surfaces of the mufiler. In some instances, a small hole has been punched in each of the end walls to aid the flow of slip. Next the muffler is removed from the bath and the excess slip allowed to drain out of its interior. It is at this precise point that prior processes of coating muifiers suffer from disadvantages.

Conventional mufflers often contain two or more offset open-ended pipes and various baflles, partitions, and compartments for directing the exhaust and absorbing sound. These battles, partitions and compartments will formpockets having openings that face in a variety of directions so that drainage of the slip is very diflicult even by continuously turning and tilting the muffler. In addition, some of the pockets, due to their shape and locations, may trap air bubbles and thereby escape being contacted with the slip.

The slip which is not removed from the mufiler will tend to form thick layers on some of the horizontal surfaces. The thick layers of porcelain enamel which result from firing of these thick-layers of slip are undesirable, because they are relatively easily knocked off the metal thus exposing parts of the mufiier. Of course, those surfaces which have escaped being coated with the slip will not be protected from corrosion after the drying and firing steps.

The method of the present invention facilitates the entry of the slip into all the chambers of a muffler during the dipping step and prevents the retention of excess slip in the chambers during the draining step. In general terms, the method comprises forming adirect flow path from each compartment through an end wall of the muffler. This maybe accomplished by drilling or punching a hole through an end wall of the mufiler and through each of the partitions to permit, free flow of slip into and out of each compartment. If desired, a drain tube I pass mufiler 10 having an outer shell 12 which is el-'- ICC may be inserted through the holes, the tube having a portion of its wall cut away at predetermined spaced locations along its length so that the bore of the tube communicates with each compartment.

After the slip has been drained out of the rnufiler through the tube or directly through the holes if no drain tube has been used the holes in the end wall and the partitions must be sealed. This may be accomplished by inserting an irnperforatetube or a solid rod through the holes, if no drain tube has been used, and sealing the imperforate tube or rod to the end wall. If a drain tube has been used, an imperforate tube or a rod is inserted into the drain tube to close the apertures therein and is then sealed to the drain tube at the ends thereof.

In view of the above, the primary object of the present invention is to provide a mufller coating method which assures that all interior surfaces of the mufller will be contacted with a slip material which will be converted on firing to the desired porcelain enamel coating.

A further object of the present invention is the provision of a muther coating method which assures that all excess slip which is used to contact the interior surface of the muffler will be removed from the muffler and thereby avoids the formation of thick coatings of slip on interior muffler parts.

Another object of the invention is the provision of a mufiier coating method which assures that drain holes formed in normally imperforate muffler parts will be effectively and simply sealed after drainage, and thereby avoid changes in the acoustical characteristics of the muffler.

A more specific object of the invention is to provide a method of preparing an interiorly compartmented article for coating with a fluid which includes the step of forming a straight passageway communicating with each compartment and with the exterior of the article.

Still another object of the invention is the provision of a mufller having a uniform porcelain enamel coating on all interior surfaces. 7

These and other objects will become apparent from a reading of the following detailed descriptionof the method of the invention taken in conjunction with the drawings in which:

FIGURE 1 is a longitudinal sectional view of a mufiler which has been provided with drain holes in accordance I with the principles of the present invention;

FIGURE 2 is an end view of the muffler of FIGURE 1; FIGURE 3 is a fragmentary side elevational view on an enlarged scale, partly broken away and partly in section, of part of the mufiler of FIGURE 1 with a drain tube positioned in the drain holes;

FIGURE 4 is an enlarged perspective fragmentary view, partly in section, of part of the mufiler of FIG- partly broken away of part of an end of the mufiler of FIGURE 3 after completion of the porcelain enameling step and illustrating a manner of sealing the drain tube which is different from that shown in FIGURE 8.

Referring now to the drawings, in particular to FIG- URES 1 and 2, there is shown aconventional multi liptical in transverse cross-section, a pair of opposed end walls 14 and 16, an inlet pipe 18 and an outlet pipe 20. A series of spaced partitions 22 divide the interior of the mufiler into a front compartment 24, three center compartments 26 and a rear compartment 28. Conventionally, the inlet pipe 18 and outlet pipe 2i will be louvered or perforated as by holes 36 along at least a portion of their length. In the embodiment illustrated, the outlet pipe 26 is provided along part of its length with an outer bafile member 32 which defines an annular space 34 between it and the outlet pipe 29. The front compartment 24 of the mufiier communicates with the inlet pipe 18 through the holes 30 but does not communicate directly with the adjacent compartment 26. The rear compartment 2 3 communicates with the outlet pipe 2% through holes 39 but does not connect directly with the adjacent compartment 26. Relatively closed end compartments, commonly 'known as resonating chambers, such as front compartment 24 and rear compartment 28, are often included in mutilers for the purpose of absorbing certain sound frequencies. The assembling of a muflier of the general type illustrated is generally carried out by first joining several of the interior parts together in gas-tight relationship, inserting these subassemblies into the outer shell 12 and then attaching the end walls 14 and 16.

It will be readily appreciated that an assembled mulfier such as that of FIGURE 1 is not easily filled with and drained of a liquid slip because of the lack of a direct flow path through all of the compartments. In particular, the front compartment 24 and the rear compartment 28 are likely to trap air during the filling step and prevent coating of all the surfaces in those compartments. During the draining step, excess slip will tend to collect in all the compartments, and particularly in 24 and 28. In practice, the assembled mufiier is usually immersed in a bath of the slip and rotated back and forth about both its longitudinal and transverse axis in an effort to coat all the interior surfaces. The rotation is repeated after the muffler is removed from the slip in an effort to drain all the excess slip through the inlet pipe 18, the outlet pipe 2% or holes which may have been punched in walls 14 and 16. This procedure is not only time-consuming but also has not been completely successful in coating all interior surfaces nor in removing all excess slip.

It has been suggested that the subassembly of partitions and pipes and the outer shell could be coated and fired separately prior to assembly. However, this procedure suffers from disadvantages in the increased cost separately coating the parts and in that chipping of the porcelain enamel may occur during the final assembly step. In addition, the well-developed conventional process of producing mufflers must be changed due to the reduced clearances between parts.

The method of coating a mufiler embodied in the present invention is illustrated in the drawings as applied to a completely assembled conventional mufiler. The preferred method, illustrated in FIGURES 1 and 2, comprises forming a straight longitudinal passageway through the mufiler so that a straight flow path is provided from the exterior of the muffler to each compartment. The passageway is easily formed by punching or drilling aligned holes 40 in each of the partitions 22 and end walls 14 and 16. The precise location of the aligned holes as will depend on the configuration of pipes, partitions and other structures in the muffler, it being desired to perforate only the partitions and end walls while leaving the pipes and baffies untouched. The size of the holes 4% should be kept as small as practicable, a diameter of three-eighths to three-quarters inch having been found suitable in many cases. The diameter will depend on variables such as the viscosity of the particular slip being used, larger holes being provided for more viscous slips. It may be necessary, with mufiiers having an interior more complicated than that illustrated, to provide a split passageway through the muffler by drilling or punching two offset series of holes, each extending from an opposite end into a common compartment. In some instances, it may be necessary to punch or drill only one end wall.

The provision of a passageway longitudinally through the mufiler by means of the holes 44 will, of itself, greatly facilitate the delivery of slip to and away from each of the compartments 2d, 26 and 28 during the dipping and draining steps respectively, and the removal of water vapor during drying of the slip. Accordingly, the provision of the holes constitutes the preferred economical embodiment of the invention. However, it may be, desirable to facilitate further the delivery and removal of slip by inserting an open-ended drain tube 42 through the holes 4%) throughout the length of the passageway as seen in FIGURE 3. The drain tube 42 tightly fits the holes 40 and has a series of axially spaced apertures 44 through its wall at locations adjacent each partition 22 and each end wall 14 and 16. The apertures 44 may be readily formed by cutting out a section of the tube wall at predetermined locations =so that as the tube is inserted through the holes 40, the apertures 44 can be positioned as desired with respect to the partitions 22 and end walls 14 and 16. Depending on the particular mufiier configuration, the drain tube 42 may be placed either in the position shown in FIGURES 3 and 4 in which the apertures 44 are adjacent each partition and end wall or in the position shown in FIGURES 5 and 6 in which the apertures straddle the partitions. In addition, it may be desirable to rotate the drain tube 42 to different positions from that shown in FIGURE 3.

The proper positioning of the tube during the dipping and draining steps will greatly facilitate the entry and removal of the slip and may eliminate entirely the necessity for rotating or tipping the muffler during these steps. The presence of the drain tube 42 in the holes 40 is particularly desirable during the draining step because it conducts most of the slip in each compartment directly to the exterior and thus avoids the sequential flow of all the slip from one compartment into an adjacent compartment. Similarly, during the drying step, the drain tube 4-2 conducts Water vapor directly to the exterior, thus avoiding condensation within the mumer and the possibility of washing off some of the slip from some of the interior surfaces.

After the muffier has been coated interiorly with the slip and drained of excess slip, it is necessary to seal the holes 40 in the end walls 14 and 16 and in the partitions 22 in order to prevent the leakage of exhaust gases from the mufiier during use and to restore the acoustical characteristics of the muffler. This may be accomplished by inserting an imperforate tube 46 or a solid rod through all the holes 40 and securing it to the end walls as by welds 48 as seen in FIGURE 7. The diameter of the tube 46 or the rod will be chosen so as to fit tightly the periphery of the holes 49 and thereby effectively restore the partitions 22 and end walls 14 and 16 to their imperforate condition.

When the drain tube 42 has been used, the passageway through the muffler may be sealed by removing the drain tube from the mufiler and inserting an imperforate tube or rod into the holes 40 in the manner just described. Preferably, however, sealing of the passageway is accomplished by tightly inserting an imperforate sealing tube 46 into the drain tube 42 throughout its length as shown in FIG. 9. When the apertures 44 straddle the partitions 22 as in the position shown in FIGURES 5 and 6, a thin arcuate hole 'will remain in each partition after insertion of a sealing tube, but it has been found that these holes do not usually affect the acoustics of the mufiier. When the apertures 44 are adjacent the partitions 22 as in the position shown in FIGURES 3, 4, 8 and 9, the holes through the partitions are, completely sealed by insertion 'tion of the imperforate condition of the mufller.

of the sealing tube 46'. Any gas which is forced between t-he tubes 42 land 46' will be prevented from escaping from the muffler by sealing the ends of the tubes to each other outside the muffler. FIGURE 9 shows an end of the tubes 42 and 46' sealed together as a result of flaring these ends, as at 47. Obviously, any suitable sealing process, such as crimping, capping or welding, could be utilized in place of the flaring step. It is desirable also to secure the drain tube 42 to the end walls, as by welds 50. Preferably Welds 50* will be applied before the firing step, either before or after the draining step.

While the sealing operations described above preferably will be effected after the drying of the slip, the sealing steps may be carried out before the slip has been dried or after the dried slip has been fused into a porcelain enamel coating. In any event, the completed mufiier will have a coating of porcelain enamel 52 on its inner surfaces as seen in FIGURES 7 and 9. As is evident from these figures, the sealing tubes 46 and 46', having been inserted after the draining of the slip, are not coated with enamel. Since the usual coating procedure involves dipping the entire mufller in a bath of slip, the exterior of the muffler will normally be enameled as well as the interior. in FIGURES 7 and 9, the exterior coating is indicated at 54. In 'FIGURE 7, the welds 48 are not shown coated because the sealing tube 46 was not inserted until after the dipping and draining steps. In FIGURE 9, the flared portion 47 of the drain tube 42 is not shown coated because the flaring step will have knocked off the coating in that area. Of course, if the muffler has been filled with slip by a method which does not involve dipping, the exterior may remain uncoated.

It will be "appreciated that the method described above provides for the rapid and positive coating of the interior of an assembled muffler with a slip, for the rapid and positive removal of excess slip, for the efficient drying of the coating of slip and for the simple and effective restora- The method requires little mechanical skill and no complicated or costly equipment or materials. It will also be appreciated that the method is applicable to the coating with porcelain enamel of compartmented articles in general.

I claim:

1. A method for preparing an assembled compartmented article having exterior walls and interior partitions for interior coating with a fluid which comprises: forming at least one straight passageway at least part way through said article by forming a hole in an exterior wall and in at least one of said partitions said holes being axially aligned; and inserting a tube having apertures in the Wall thereof at predetermined longitudinal positions into said passageway whereby one of said apertures may be positioned in each of said compartments.

2. A method for coating the interior surfaces of an assembled compartmented article having exterior walls and interior partitions comprising: forming a straight passageway at least part way through said article by forming a hole in an exterior wall and in at least one of said partitions said holes being formed in axial alignment; inserting a tube having apertures in the wall thereof atpredetermined longitudinal positions into said passageway so that at least one aperture is positioned in each compartment; introducing fluid into the compartments of said article; removing at least some of said fluid from said compartments through said tube; closing said apertures by inserting an imperforate member into the length of said tube; and sealing said imperforate member to said tube.

3. A method as in claim 2 in which said apertures in said tube are so spaced that when said tube is inserted in said passageway, an aperture is adjacent each partition.

4. A method for preparing a compartmented mufiier having end walls and spaced partitions therebetween for interior coating with porcelain enamel which comprises:

w forming a longitudinal passageway at least part way through said muffler by forming at least one hole through an end wall and through at least one partition whereby each compartment communicates with the exterior of the muffler through a straight flow path; and inserting a tube having apertures in the wall thereof at predetermined longitudinal positions into said passageway whereby at least one aperture may be positioned in each compartment.

5. A method as in claim 4 in which a hole is formed in each partition and in each end wall and in which said holes have a common axis.

6. A method for coating with a porcelain enamel slip the interior surfaces of a compartmented mufiler having end Walls and spaced partitions therebetween forming said compartments comprising: forming a longitudinal passageway from each compartment through an end wall to the exterior of said muffler; inserting a tube having longitudinally spaced apertures therein through said passageway; introducing slip into said compartments; removing at least some of said slip from said compartments through said tube; and sealing said tube against the further passage of fluid into or out of said compartments.

7. A method as in claim 6 in which the step of forming said longitudinal passageway includes the step of forming at least one hole through an end wall and through at least one partition and the step of sealing said tube by tightly inserting an imperforate member therein.

8. A method for coating with a porcelain enamel slip the interior surfaces of a compartmented mufller having end walls and spaced partitions therebetween forming said compartments comprising: forming a longitudinal passageway at least part way through said mufller by forming at least one hole through an end wall and through at least one partition whereby each compartment communicates with the exterior of the muffler through a straight flow path; inserting a tube having apertures in the wall thereof at predetermined longitudinal positions into said passageway whereby said apertures are positioned at said partitions and at said end wall; introducing fluid into said compartments; removing at least some of said fluid from said compartments through said tube; closing said apertures by inserting an imperforate member into the length of said tube; and sealing said imperforate member to said tube at the ends thereof.

9. A method as in claim 8 in which a hole is formed in each partition and in each end wall and in which said holes have a common axis.

10. A method asin claim 8 further including the step of securing said tube to said end wall.

11. An interiorly coated compartmented mufller comprising: spaced end walls; an imperforate side wall sealed to said endwalls; at least one partition sealed to said side wall intermediate said end walls; a porcelain enamel coating on the inner surface of said end and side walls and on the surfaces of said partition; a substantially straight tube having at least one aperture in the side thereof extending through at least one of said end walls and through said partition and being in substantially fluid-tight engagement with said end wall and said partition; and a substantially straight imperforate member extending through said tube and being in substantially fluid-tight engagement therewith along their opposed surfaces.

12. A mufller as in claim 11 in which said tube and said imperforate member are substantially parallel to the longitudinal axis of said mufller.

References Cited in the file of this patent UNITED STATES PATENTS 2,395,005 Kuhn Feb. 19, 1946 2,598,756 Brightly et al June 3, 1952 3,082,841 Powers Mar. 26, 1963 3,107,748 Placek Oct. 22, 1963 FOREIGN PATENTS 126,776 Australia Feb. 10, 1948 

1. A METHOD FOR PREPARING AN ASSEMBLED COMPARTMENTED ARTICLE HAVING EXTERIOR WALLS AND INTERIOR PARTITIONS FOR INTERIOR COATING WITH A FLUID WHICH COMPRISES: FORMING AT LEAST ONE STRAIGHT PASSAGEWAY AT LEAST PART WAY THROUGH SAID ARTICLE BY FORMING A HOLE IN AN EXTERIOR WALL AND IN AT LEAST ONE OF SAID PARTITIONS SAID HOLES BEING AXIALLY ALIGNED; AND INSERTING A TUBE HAVING APERTURES IN THE WALL THEREOF AT PREDETERMINED LONGITUDINAL POSITIONS INTO SAID PASSAGEWAY WHEREBY ONE OF SAID APERTURES MAY BE POSITIONED IN EACH OF SAID COMPARTMENTS. 